The present invention relates to a class of reagents for colorimetrically determining formaldehyde in solution or in air, and to the use of such a reagent for monitoring exposure to formaldehyde.
Formaldehyde is an important chemical which is widely used in various industries, such as plastics, textiles, etc. Because of increasing concern over safety and health hazards presented by exposure to formaldehyde vapors in air and governmental regulations limiting the permissible level of formaldehyde vapors in the workplace environment, industries require an effective and reliable way to monitor formaldehyde levels in the workplace environment and to control exposure to hazardous formaldehyde concentrations.
Various monitoring devices have been developed for monitoring exposure by individuals to formaldehyde. One popular type of monitoring device is a dosimeter badge, which is intended to be worn by persons who work in an area which may be contaminated with formaldehyde vapors. Various ways are provided for obtaining a reading of the formaldehyde exposure from the badge. However, the commercially available badges which have been developed for monitoring formaldehyde have been subject to one or more disadvantages or limitations, including expense, lack of reliability, and inability to provide a continuous direct readout of formaldehyde exposure. Many of these disadvantages and limitations are due to the chromophoric reagent used in the dosimeters.
Several reagents for colorimetric determination of formaldehyde have been described in the literature. The most important ones are described in Table 1 below.
TABLE 1 ______________________________________ Conventional Colorimetric Reagents for the Determination of Formaldehyde Refer- Reagent Comments ences* ______________________________________ Chromotropic Very sensitive and selective; 1-2 Acid (and however, it is slow and requires variations of) testing in concentrated acid. Phenol interferes in some procedures. Schiff's Reagent Very sensitive and reasonably 3 and ref- selective. Utilizes cumbersome erences reagents. The color formed is not therein, stable. The reagents are not stable. 4-5 MBTH (3-meth- Very sensitive reagent for ketones 6-7 yl-2-benzothi- and aldehydes, (but is not selec- azolone tive to formaldehyde. The reagent hydrazone) is unstable. Used mainly for TOTAL aldehydes in air. Potassium ferri- Very sensitive and reasonably 8 cyanide phenyl- selective; The reagent is, however, hydrazine. very unstable. Silver chro- Reasonably sensitive. However, 9 mate-ethylene the reagent is unstable and can be diamine used only in non-acidic solutions. Nickel cyanide Sensitive and reasonably selective; 10 and dimethyl however, it takes a long time to glyoxime. develop the full color. ______________________________________ *References 1. Taylor, D. G. (Manual Coordinator), "NIOSH Manual of Analytical Methods," Vol. I, Section 125 (1977). 2. Knox, S. E. and Hee, S. Q., Am. Ind. Hyg, Assoc., 45 (5), 325-328 (1984). 3. Walker, J. F., "Formaldehyde," Chapt. 20, 3rd Ed., ACS, New York, 1964 4. Miksch, R. R., Anthon, D. W., Fanning, L. Z., Hollowell, C. D., Revzan K. and Glanville, J., Anal. Chem., 53, 2118-2123 (1981). 5. Kuijpers, A. T. J. M. and Neele, J., Anal. Chem., 55, 390-391 (1983). 6. Miksch, R. R. and Anthon, D. W., Am. Ind. Hyg. Assoc. J., 43, 362-365 (1982). 7. Katz, M. (ed.), "Methods of Air Sampling and Analysis," APHA Intersociety Committee, 2nd Ed., Am. Pub. Health Assoc., Washington, D.C. 20036 (1977). 8. Schrvver, S. B., Pres. Roy. Soc. London (B), 82, 226 (1910). 9. Neto c. Chem. Abst. 54, 1160 (1960). 10. West, T. W. and Sen, B., Anal. Chem., 27, 1460 (1955).
However, the above-noted known colorimetric reagents all suffer from at least one of the following disadvantages:
1. They form color very slowly. PA1 2. The reagents are unstable. PA1 3. The reagents cannot be easily used in the field. PA1 4. The reagents cannot be adapted to dry-chemistry application. PA1 5. The reagents are non-selective to formaldehyde.
The present invention provides a colorimetric reagent which can visibly show the presence of formaldehyde, and which is useful in various applications, such as for example in a direct reading colorimetric gas dosimeter. The availability of a colorimetric reagent which can visibly show the presence of formaldehyde can help even unskilled personnel determine whether they are present in a dangerous environment.